This invention relates to a straddle, and in particular a straddle for use in selectively isolating a section of tubing. The invention also relates to a method of isolating a section of tubing.
In the oil and gas exploration and production industries, subsurface hydrocarbon-bearing formations are accessed via casing-lined wellbores. The lower section of a bore, which intersects the hydrocarbon-bearing formation, is typically lined with perforated xe2x80x9clinerxe2x80x9d, oil and gas flowing into the bore through the perforations. The location of the perforations is predetermined on the basis of surveys, to ensure that only selected formations ate in fluid communication with the bore. Over the life of a well it may occur that the properties of particular formations change, for example the pressure in a formation may fall, or a formation may begin to produce an unacceptably high volume of water. In these circumstances it is known to run straddles into the liner, these straddles being sections of tubing with sealing arrangements at either end. A straddle may be located within the section of liner intersecting the problem formation, and the seals then set to isolate the section of liner between the seals. However, existing straddles are problematic to set, and the requirement to accommodate the seals and a seal setting mechanism result in a significant loss in bore cross section, which reduces the production capacity of the well and also makes it more difficult to access the section of well beyond the straddle.
It is among the objectives of embodiments of the present invention to provide an improved straddle which obviates or mitigates these difficulties.
According to the present invention there is provided a method of isolating a section of downhole tubing, the method comprising:
running a length of expandable tubing into a tubing-lined borehole and positioning the expandable tubing across a section of tubing to be isolated; and
deforming the expandable tubing by increasing the diameter of at least portions thereof to sealingly engage the tubing and to isolate said section.
According to another aspect of the present invention there is provided apparatus for use in isolating a section of tubing-lined borehole, the apparatus comprising: a length of expandable tubing; and an expander device including a radially extendable member for deforming at least portions of the expandable tubing to increase the diameter of said portions to sealingly engage a section of tubing to be isolated.
Preferably, the expandable tubing is deformed by compressive plastic deformation or yield of the tubing and a localised reduction in tubing wall thickness with a subsequent increase in tubing diameter. Conveniently this is achieved by rolling expansion, that is the expander device is rotated within the expandable tubing with an expander member in rolling contact with an inner face of the expandable tubing.
The deformation of the expandable tubing preferably creates an annular extension. This annular extension may extend over all or a substantial portion of the expandable tubing, or may be restricted to a selected portions of the expandable tubing on either side of the section of tubing to be isolated. The former arrangement will be more secure, but would be more difficult to remove from the tubing.
The tubing lining the bore may be casing or liner, or may be secondary tubing, such as production tubing itself positioned within a section of casing or liner.
The expandable tubing may include relatively ductile portions corresponding to the portions of the tubing to be expanded. These portions may be welded or otherwise secured to portions of less ductile tubing.
The expandable tubing is preferably initially cylindrical.
Preferably, the expander device comprises a body carrying a plurality of expander roller members. Most preferably, a plurality of the expander members are radially extendable. Preferably, the expander members are fluid activated, for example the members may be operatively associated with a piston. In one embodiment, the members may be mounted on respective radially movable pistons and in other embodiments the members may have tapered ends for engaging cones or wedges coupled to an axially movable piston.
The expandable tubing may carry seal bands on an outer surface thereof. The seal bands may comprise at least one of an elastomeric seal and a hand of relatively ductile metal, such as copper or a tin/lead alloy.
The expandable tubing may carry grip bands on an outer surface thereof. The grip bands may comprise relatively hard elements, such as balls, chips or grains, held in a matrix, whereby the elements bite into the relatively soft material of the tubing and the expandable tubing on deformation of the expandable tubing. In other embodiments the relatively hard elements may be in a form other than bands.